Brave locals rescued three children from the wreckage of a helicopter crash before a farmer pulled the mangled aircraft out of the mouth of the Kekerengu River.

Two people were killed in the crash and three others - the children - were seriously injured before they were later airlifted separately to Wellington Hospital.

Investigators will comb through the wreckage tomorrow morning as they work to understand the circumstances that led to the crash.

Fire and Emergency New Zealand (Fenz) operational insurance team member Darryl Papesch believed those rescued were children.

He was one of the first responders on the scene after visiting the local volunteer fire brigade and said locals had pulled everyone out of the wreck by the time he arrived.

"We were having conversations with them, not a proper conversation but they knew their names and how old they were," Papesch said.

"The three people injured were young ... they weren't adults, I'd say children, definitely children."

He said locals removed the five occupants before a local with a tractor pulled the helicopter up the beach and well-clear of the water.

"The locals were outstanding, in a chaotic situation they were outstanding.

"All three agencies, Fenz, police, St John, all worked together and just got on with it."

• Two people confirmed killed in Kaikoura helicopter crash

Local Ian Mehrtens, who was one of the first people at the scene, told Heather du Plessis-Allan helicopters often head to the beach in summer, but this one landed badly. 

"Poor old helicopter was on its side and pretty well smashed up, bits and pieces everywhere, and a couple of the passengers were crying out in pain of course."

The Transport Accident Investigation Commission has opened an inquiry - and is sending three people to the site tomorrow morning.

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